DENVER, Colorado (CNN) -- Sen. Barack Obama's acceptance of the Democratic Party's presidential nomination may be historic in many ways. One of them is the size of the audience at Invesco Field.

More than 75,000 people packed into the football stadium in Denver, Colorado, to hear Obama's historic speech as the first African-American Democratic presidential nominee.

The enormity of the crowd was borne out by the gridlock that greeted them as they left the stadium. Attendees shuffled along like herds of cattle, moving inches at a time, as they attempted to leave the grounds.

"What his whole campaign is about is bringing people together," said iReporter William Gilbane III. "The mix of people -- young, old, gay, straight, white, black -- everything you could imagine was represented in the crowd and it was just really, really exciting." Watch Gilbane describe the scene inside the stadium »

Local authorities worked with the Secret Service to get as many people into the stadium as possible. Obama said he chose to speak Thursday at Invesco Field, which seats 76,000 people, to make sure "everybody who wants to can come."

Some attendees stood shoulder-to-shoulder on the stadium floor for hours, mingling among the likes of celebrities such as Spike Lee, Farrah Fawcett, Susan Sarandon and Oprah Winfrey.

By midday, thousands stood in the warm temperatures to wait in lines that were nearly six miles long, according to local police. The lines snaked around ramps and onto the Auraria Boulevard overpass, which leads to Invesco Field. Watch thousands walk toward the stadium »

A group of transportation volunteers in orange T-shirts with the convention logo walked toward the front of the line. They called out, "What time is it?" People responded, "Obama time!"

Les Spencer and Tony Viessman, lifelong Democrats who call themselves "Rednecks for Obama," went through the crowds, talking about their support for the Illinois senator.

"Don't be afraid to vote for Obama!" Les said.

Their motto, according to Les and Tony, is "workin' for the man who'll do more for the workin' man."

Obama's speech fell on the 45th anniversary of Dr. Martin Luther King Jr.'s "I Have a Dream" speech. Two of King's children, the Rev. Bernice King and Martin Luther King III, participated in a tribute to their father at the convention.

The crowd also heard from former vice president Al Gore, New Mexico Gov. Bill Richardson and party chairman Howard Dean.